JPH0218059A - Thermal head - Google Patents

Abstract

PURPOSE:To enable a uniform and sufficient pressing force to be easily obtained and stably a high-quality image with uniform density by adjusting the gap between a head base and a heat-radiating plate according to the waviness of the base. CONSTITUTION:Thin film sheet form correcting members 21, 22 as gap-adjusting means are inserted between a head base 15 and a heat-radiating plate 11. The sizes and inserting positions of the correcting members 21, 22 are determined based on the measurement of the surface shape of a heat generating line 16. When a platen roller 1 is pressed against the head base 15 in the condition where the correcting member 21 is inserted between the bottom surface of the head base 15 having a single recess and the heat-radiating part 11, the head base 15 is pressed upward by the correcting member 21 making contact with the bottom surface part of the recess of the head base 15, whereby a pressing force is increased correspondingly to a compression of a platen rubber 4. The pressing force exerted on the head base 15 at a position is decreased as the position is remote from the position of the recessed part of the head base 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head used as a head for various thermal printers such as a heat sublimation type, a heat melting type, and a heat-sensitive coloring type.

[Prior Art] FIG. 13 is a diagram showing the recording principle of a thermal dye sublimation printer. Reference numeral 1 designates a platen roller, which is composed of a rotating shaft 2, a core metal part 3 fitted into the rotating shaft 2, and a platen rubber part 4 attached so as to cover the outer peripheral surface of the core metal part 3. There is. Reference numeral 5 denotes a thermal head, which has a configuration in which an array of heating resistors is arranged in a line along the axial direction of the rotating shaft 2.

The thermal dye sublimation printer configured as described above forms a visible image in the following manner. An ink sheet 6 coated with a sublimable dye and an image receiving paper 7 are placed one on top of the other with the ink sheet 6 facing the thermal head 5 side, and are pressed against the thermal head 5 by the outer peripheral surface of the platen roller 1. In the pressed state, the heating resistor array of the thermal head 5 is selectively heated to transfer the sublimable dye onto the surface of the image receiving paper 7. As a result, a visible image is formed on the image receiving paper 7.

The above-mentioned thermal sublimation recording method is characterized by controlling the amount of heat generated by the thermal head, adjusting the amount of dye transferred to the image receiving paper 7, and easily forming a gradation record with shading on the image receiving paper 7. At the point. Further, by using ink sheets of three colors, yellow magenta and cyan, and transferring each color onto the image receiving paper 7 in an overlapping manner, it is possible to record in any color on the image receiving paper 7. Because of these characteristics, thermal dye sublimation printers are seen as promising terminal devices for outputting photo-like full-color prints in combination with various video equipment.

As mentioned above, thermal dye sublimation printers have the excellent feature of being able to easily perform full-color recording, but on the other hand,
It has the following drawbacks.

FIG. 14 is a perspective view schematically showing a thermal head 5 used in a conventional thermal dye sublimation printer. In the figure, 11 is a heat sink, 12 is a ceramic substrate, 13 is a linear heating resistor array, and 14 is a protective film. Note that the arrow shown in the figure indicates the printing width direction. As shown in the figure, a ceramic substrate 12 and a heating resistor array 13
The head substrate 15 made up of the thermal head 5 and the protective film 14 has "undulations" on the order of several tens of microns along the line direction of the thermal head 5. This "undulation" is caused by the "warpage" of the ceramic substrate 12 that constitutes the head substrate 15. Therefore, "warpage" occurring in the ceramic substrate 12 cannot be avoided due to the current manufacturing technology.

FIG. 15 is a side sectional view showing the relationship between the platen roller 1 and the thermal head 5 having the above-described "wavy" head substrate 15. As shown in FIG. As is clear from the figure, when the platen roller 1 is brought into pressure contact with the head substrate 15 having "undulations", uneven portions appear on the head substrate 15.

As a result, considerably stronger pressing force (adhesion force) is applied to the ink sheet 6 and image receiving paper 7 pressed by the convex portions S1 and S2 compared to other portions. Conversely, the convex portion Sl,
Sufficient pressing force is not applied to the portions pressed other than S2. For this reason, the dye-applied surface of the ink sheet 6 and the image receiving paper 7
It is not possible to bring them into sufficient contact with each other with uniform force, and in areas where the adhesion is weak, recording dots may be chipped or areas where the dye is not transferred may occur.

FIG. 16 is a plan view showing an example of an image formed using the thermal head 5 and platen roller 1 shown in FIG. 15. As shown in the figure, a striped shading pattern occurs in a direction parallel to the sub-scanning direction (recording paper conveyance direction) of the screen. The shaded portion in the figure is the convex portion S of the head substrate 15.
This is the part corresponding to L and S2. In addition, the image in areas other than the shaded area is not recorded at all or is faded in white.

As a solution to these shortcomings, for example, "Development and application of a dye-sublimation heat-sensitive transfer color printer" (Dainippon Printing Co., Ltd.) Japan Industrial Technology Center Seminar, T-1
830, I) I), 1-8 (1986), a soft material is used as the platen rubber part 4, and the pressing force of the platen roller 1 against the thermal head 5 is made large, so that the platen rubber part 4 is There is a means for deforming the ink sheet 6 and the recording paper 7 to absorb variations in adhesion force and to obtain uniform adhesion force.

Another solution is to manufacture the platen roller 1 into a shape that corresponds to the undulations of the head substrate 15 of the thermal head 5.

[Problems to be Solved by the Invention] However, each of the above-mentioned solving means has the following drawbacks. In the method of adjusting the hardness and pressing force of the platen rubber part 4 to make the adhesion uniform, if the platen rubber part 4 is made too soft, the heat-sensitive resistor line of the thermal head 5 will dig into the platen rubber part 4, and the ink sheet will be damaged. 6 and the running properties of the recording paper 7 are impaired. Further, when the soft platen rubber portion 4 is used, the suppression width becomes wider and the pressing force per unit area applied to the ink sheet 6 and the recording paper 7 becomes smaller. As a result, the sharpness of the recorded dots decreases, resulting in an image with poor "cutting". Note that if the platen rubber part 4 is made harder, the pressing force per unit area will increase and a clear image can be obtained, but uneven density will be noticeable and the pressing surface of the thermal head will be severely damaged by mechanical wear. Become. Therefore, in reality, the combination of hardness and pressing force of the platen rubber portion 4 is selected and used to such an extent that density unevenness is relatively inconspicuous and the sharpness of the image is not impaired. Therefore, the characteristics of the thermal sublimation recording method cannot be fully utilized, and high quality images have not yet been achieved.

Furthermore, the idea of manufacturing and using a platen roller with a diameter that corresponds to the "undulations" of the head substrate 15 is ideal as a means to suppress the occurrence of density unevenness, but it is also The roller has to be manufactured, and the price of the platen roller becomes extremely high.

Furthermore, when the thermal head is replaced due to damage or expiration of its life, the platen roller must also be replaced in accordance with the replacement of the thermal head, making it difficult to put it into practical use.

The above-mentioned drawbacks are not limited to thermal dye sublimation printers, but also occur in printers using thermal heads, such as thermal color printers, hot melt forging printers, and the like.

Therefore, an object of the present invention is to enable a thermal head to easily obtain uniform and sufficient adhesion even if the head substrate has undulations, and to produce high-quality images without density unevenness. To provide a stable and inexpensive platen roller for a thermal printer.

[Means to solve the problem]

The present invention has taken the following measures to solve the above problems and achieve the objectives. That is, a gap adjusting means is provided for adjusting the gap between the head substrate and the heat sink according to the "undulations" of the head substrate.

[Effect] By taking the above measures, the following effects are achieved.

That is, since the pressing force of the platen roller against the head substrate becomes uniform, a uniform adhesion force acts on the recording paper, and the recording density of the printed image becomes uniform.

[Embodiment] FIGS. 1(a) and 1(b) are diagrams showing a first embodiment of the present invention, FIG. 1(a) is a perspective view of a thermal head 20, and FIG. 1(b) is a perspective view of a thermal head 20. 7 is a front view showing a state in which an ink sheet 6 and an image receiving paper 7 are held under pressure between a thermal head 20 and a platen roller 1. FIG. Note that in FIGS. 1(a) and 1(b), the same parts as in FIGS. 13 to 15 are designated by the same reference numerals.

As shown in FIG. 4A, a head substrate 15 having a heating line 16 on which a heating resistor array 13 is disposed is fixed onto a heat sink 11 by a substrate holding plate 17. Thin film sheet-like correction members 21 and 22 are inserted between the head substrate 15 and the heat sink 11 as gap adjusting means. The dimensions and insertion positions of the correction members 21 and 22 are determined by measuring the shape of the surface of the heating line 16.

FIGS. 2(a) and 2(b) schematically show a thermal head 20.
(a) is a front view showing the state before the platen roller 1 is pressed against the thermal head 20, and (b) is a front view showing the state before the platen roller 1 is pressed against the thermal head 20. FIG. 3 is a side view showing a pressed state.

3(a) and 3(b) are diagrams showing the case where the correction member is not inserted into the thermal head 20, and (a) shows the platen roller 1.
is a diagram showing the state before being pressed into contact with the thermal head 20,
(b) is a diagram showing a state in which the platen roller 1 is pressed against the thermal head 20.

In FIGS. 2(a)(b) and 3(a)(b), in order to simplify the explanation, "
The undulations are shown as one dent.

With the correction member 21 inserted between the bottom surface of the head substrate 15 having one "dent" shown in FIG. 2(a) and the heat sink 11, the platen roller is moved as shown in FIG. 2(b). When the platen roller 1 is pressed against the head substrate 15, the distribution of the pressing force newly applied to the head substrate 15 from the platen roller 1 due to the insertion of the correction member 21 becomes as shown in FIG. 4(b).

The head substrate 15 is pushed up from below by the correction member 21 that comes into contact with the bottom portion of the "dent" in the pinch head substrate 15, and becomes larger by the amount that the platen rubber 4 is compressed. Then, the further away from the position of the concave portion of the head substrate 15, the less the pressure force applied to the head substrate 15 becomes.

When the platen roller 1 is pressed against the thermal head 20 without interposing a correction member as shown in FIGS. 3(a) and 3(b), the pressure contact force distribution becomes as shown in FIG. 4(a). In other words, the position of the "dent" portion of the head substrate 15 is the smallest,
The further away from the "dent" area in the line direction, the stronger the pressing force exerted on the head substrate 15 becomes.

The composition of the pressure contact force distribution when the correction member 21 is not attached as shown in FIG. 4(a) and the pressure contact force distribution when the correction member 21 is inserted as shown in FIG. 4(b) is as follows. As a result, the uneven portions cancel each other out, resulting in a shape similar to that shown in FIG. 4(C).

FIG. 5(a) is a diagram showing the shape of the surface of the heating line, and FIGS. 5(b) and 5(c) are diagrams showing the density state in the line direction of the sample printed by the thermal head. be. Note that the actual heat generating line 16 often has a plurality of "dents". Therefore, the method for determining the insertion position and dimensions of the correction member 21 in such a case is shown in FIGS. 1(a) and 5(b) and FIGS.
).

When measuring the surface shape of the heating line 16, for example, the fifth
The state is as shown in Figure (a).

The horizontal axis of the figure shows the position in the length direction of the heat generating line 16, and the vertical axis shows the degree of depression on the surface of the heat generating line 16. In the figure, Ll, L2. The portion indicated by L3 is recessed by a maximum of 25 μm.

Figure 5(b) shows "undulations" like Figures 5(a) and (b).
The graph shows the density in the line direction when solid printing is performed using the thermal head 20 equipped with the heat generating line 16 having the following characteristics. L2 in FIG. 5(a). In the portion indicated by L3, the density decreases in a concave shape, and uneven recording density occurs. Therefore, correction members 21, 22, etc. are inserted at the position where the heat generating line 16 forms a concave shape.

Correction member 21.2 for insertion into the thermal head 20
The second dimension is determined from the surface shape of the heating line 16 shown in FIG. 5(a). The depth of the L2 "dent" is up to 25 μm and the width is about 15+++ m. Therefore, the correction member 21 inserted at the position L2 of the head substrate 15
The thickness is 25 μm to cancel the 25 μm depth of the
~30 μm, and the width is 10 μm less than the width of the “undulation”.
~14IIJI. The thickness of the correction member 22 inserted at the position L3 of the head substrate 15 is set to 15 to 20 μm using the same method as the method for determining the size of the correction member 210 described above.

The width is determined to be 7 to 9B. And these correction members 21
．． 22 was made using a thin film sheet of a certain thickness, and the first
As shown in Figures (a) and (b), the head substrate 15 and the heat sink 1
Insert between 1 and 1.

When printing is performed using the thermal head 20 into which the correction members 21 and 22 are inserted in this manner, a constant density distribution is obtained as shown in FIG. can.

Hereinafter, a modification of the first embodiment will be described.

6(a) and 6(b), a thermosetting adhesive 23 is interposed between the correction member 21 and the back surface of the head substrate 15, and by energizing the heating resistor array of the head substrate 15 during print recording, This is an example in which the thermosetting adhesive 23 is heated and cured, and the correction member 21 is stably fixed to the head substrate 15 by the bonding force of the thermosetting adhesive 14. Note that the correction member 21 may be fixed to the heat sink 11 side using the thermosetting adhesive 23 described above.

7 and 8(a) and 8(b), a protrusion 24 corresponding to the shape of the correction member is integrally formed on either the heat sink 11 or the pressure contact surface of the head substrate 15. This is an example.

9(a) and 9(b) show that a large number of pin holes 31 are formed in the heat dissipation plate 11, and when the correction member 21 is inserted between the heat dissipation plate 11 and the head substrate 15, the protrusion jig 32 is pinned. In this example, the head substrate 15 is pushed up by inserting the correction member 21 into the gap. In this way, the insertion operation of the correction member 21 becomes easy.

[Second Embodiment] FIGS. 10(a) and 10(b) are diagrams showing a second embodiment of the present invention. This embodiment is an example in which a correction screw as a gap adjustment means protruding from a heat sink is used instead of a correction member to prevent density unevenness during printing due to "waving" of a heat generation line.

As shown in FIGS. 10(a) and 10(b), the head substrate 150
A large number of screw holes 33 are formed in the heat sink 11 directly below the heat generating line (not shown) in parallel with the heat generating line. and,
By screwing a correction screw 34 into this screw hole 33 with a driver 35, a predetermined portion of the head substrate 15 is pushed up. At this time, the height at which the head substrate 15 is pushed up by the correction screw 34 is determined by measuring the shape of the surface of the heating line. Thus, according to this embodiment, as shown in FIG. 10(b), the same effect as in the first embodiment is achieved by the correction screw 34 interposed between the heat sink 11 and the head substrate 15 during printing. be effective.

[Third Embodiment] FIG. 11 and FIG. 12 are diagrams showing a third embodiment of the present invention. In this embodiment, as shown in FIGS. 11 and 12, a large number of piezoelectric elements 40 are arranged in a row on a heat sink 11 located directly under a heat generation line 16 of a head substrate 15, and The piezoelectric element 40 is configured to be displaced in a direction perpendicular to the head substrate 15 by selectively applying a voltage to the piezoelectric element 40 . When correcting the "undulations" on the surface of the heat generation line 16, a required voltage is selectively applied to the piezoelectric element 40 corresponding to the recess of the heat generation line 16 based on the shape of the surface of the heat generation line 16. For example, the piezoelectric element 40 is displaced to a desired state. Thereby, the piezoelectric cord 40 pushes up the head substrate 15, so that the same effect as in the embodiment described above is achieved.

Note that the present invention is not limited to the embodiments described above, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] According to the present invention, the gap between the head substrate and the heat sink is
By providing a gap adjustment means for adjusting according to the "undulations" of the head substrate, even if the thermal head has a head substrate with "undulations",
It is possible to provide an inexpensive platen roller for a thermal printer that can easily obtain uniform and sufficient adhesion and can stably obtain high-quality images without density unevenness.

[Brief explanation of the drawing]

FIGS. 1(a), (b) to 5(a), (b), and (C) are diagrams showing a first embodiment of the present invention, and FIG. 1(a) shows a case in which a correction member is inserted into a thermal head. FIG. 1(b) is a perspective view showing a state in which a correction member is inserted, and FIG.
)(b) is a side view showing a state in which a correction member is inserted into a simulated thermal head, and FIGS. 3(a) and 3(b) are a side view showing a state in which a correction member is not inserted into a simulated thermal head. 4(a) to 4(c) are diagrams showing the distribution of the pressure contact force acting on the head substrate, FIG. 5(a) is a diagram showing the shape of the surface of the heating line, and FIG. 5(b) is a front view. ) and (C) are diagrams showing the density state in the line direction of a sample printed by a thermal head. FIGS. 6(a) and 6(b) are front views showing a modified example in which the correction member is fixed with a thermosetting adhesive, and FIGS. 7 and 8(a) and (b) correspond to the correction member. FIG. 9 (a
) and (b) are diagrams showing a modification in which the correction member is inserted into the thermal head using a jig. Figure 10 (a
) and (b) are diagrams showing the configuration of the second embodiment of the present invention;
FIG. 10(a) is a sectional view showing a state in which the head substrate is pushed up to a required height by a correction screw, and FIG. 10(b) is a front view of the thermal head. 11 and 12 are diagrams showing a third embodiment of the present invention, FIG. 11 is an exploded perspective view of a thermal head incorporating a piezoelectric element as a gap adjustment means, and FIG. 12 is a state in which the thermal head is used. FIG. 13 to 15 are diagrams showing an example of the configuration of a conventional thermal head, and FIG. 16 is a diagram showing density unevenness of a sample printed by the conventional thermal head. DESCRIPTION OF SYMBOLS 1...Platen roller, 2...Rotating shaft, 3...Core part, 4...Platen rubber part, 5.20...Thermal to/from, 6...Ink sheet, 7...・Receiving paper,
11... Heat sink, 12... Ceramic board, 13.
...Heating resistor line, 14...Protective film, 15...
Head substrate, 16... Heat generation line, 17... Substrate holding plate, 21.22... Correction member, 23... Thermosetting adhesive, 32... Protrusion jig, 33... Screw Hole, 34... Correction screw, 35... Driver, 40
···Piezoelectric element. Applicant's representative Patent attorney Atsushi Tsuboi Figure (b) (c) (mm) Figure 11 Figure (a) (b) Figure 13 Figure

Claims (1)

[Claims] In a thermal head in which a heat dissipation plate is brought into contact with the back of a head substrate in which a heat generating resistor array is formed in a straight line on an insulating substrate, the gap between the head substrate and the heat dissipation plate is formed into the "undulations" of the head substrate. A thermal head characterized by being equipped with a gap adjustment means for adjusting accordingly.